In all three months it had a background noise volume of around 10
between spikes.
And in all three months the spikes didn’t last very long.
So it appears U-PGH-NET-AS has some sort of chronic
problem with letting spam out, but UPMC
does notice whenever it gets bad and fixes it pretty quickly.
This latest #1 was actually worse for this ASN, however,
since the previous two times it spammed about a third of
the top 10 total, and this time it spammed 42.1%.

Top volume is also up an order of magnitude, from 90 to above 1,000.
UPMC seems to have something to fix.